1. Field of the Invention
The present invention relates to the field of downhole operations involving a Christmas tree. More specifically, the present invention, in an exemplary embodiment, relates to a system and method of operation using a tree saver with Christmas trees. More specifically still, the present invention, in an exemplary embodiment, relates to a system and method of operation using a tree saver with Christmas trees located subsea.
2. Description of the Related Art
Christmas trees are well known in the prior art, including use in subsea production of oil and gas, and are used in undersea operations to seal and control a well. Christmas trees typically have a series of pipes and valves that are situated on the well head after drilling of the well has been completed, and often extend vertically from the well head. Typically, the Christmas tree is coupled at its lower end to the well casing and (at least usually) to a string of tubing within the casing. Christmas tree assemblies further typically have one or more horizontal production outlets.
A tree saver is typically a heavy gauge piece of pipe which in some embodiments may be approximately two meters long and five centimeters in diameter and which is inserted through the Christmas tree and into the well tubing to prevent fracturing fluid from wearing away at the valves and parts of the Christmas tree. The tree saver may be held in place by means of a bolted coupling and rubber sleeve or by pressure in the well.
U.S. Pat. No. 4,632,183 issued to McLeod for an xe2x80x9cINSERTION DRIVE SYSTEM FOR TREE SAVERSxe2x80x9d is illustrative and discloses an insertion drive system for a well head tree saver that includes a pair of parallel, spaced beams, a lower one of which is attached to the tree. High pressure tubing is held by the upper beam and is inserted into or withdrawn from the tree by motor driven mechanical jack assemblies which lower or raise the upper beam relative to the lower beam. As motor means rotates the shafts the interaction between the upper ends of the shafts and the captive nuts cause the upper beam and its supporting apparatus to move downwardly to insert the tube through the Christmas tree. In the embodiments disclosed, once the tube has been lowered to its desired position a lock ring threadably engages a screw collar to lock the tree saver mandrel tube in place. There is no suggestion, motivation, or teaching to use pressure to lower the tree saver mandrel tube into place or to position the tree saver mandrel tube into a predetermined position extending into a tubing hanger associated with the tree.
U.S. Pat. No. 4,023,814 issued to Pitts for xe2x80x9cTREE SAVER PACKER CUPxe2x80x9d is also illustrative and discloses a packer cup assembly which attaches to the lower end of the mandrel in the tree saver which is itself attached to a Christmas Tree of a well head or the like. The assembly is tubular in configuration and comprises a metal part with internal threads at one end and a thinner walled part at its other end. The outer diameter of the lower end of the metal part is less than the outer diameter of the threaded end part in order to permit an elastomeric sleeve to fit over and extend beyond the reduced diameter end part of the metal part. The outer end of the elastomeric sleeve is flared outwardly and then tapered inwardly to facilitate entry into a string of tubing or the like. The other end of the elastomeric sleeve is bonded to the outer surface of the metal part. There is no suggestion, motivation, or teaching to use pressure to lower a tree saver into place or to position the tree saver into a predetermined position extending into a tubing hanger associated with the tree.
In the prior art, certain processes, by way of example and not limitation including cementing processes, are often used to plug a well once the well is no longer to be in service. It is desirable to be able to salvage, refurbish, and reuse subsea wellheads and Christmas trees. However, contaminants such as cement can get into the Christmas tree, fouling the Christmas tree and making it unsuitable for further use.
As is well known in the art, tree savers are used to protect the wellhead from pressure and, in the case of fracturing operations, from fracturing fluids. However, in the prior art, tree savers used during well completion processes provide no protection from cement getting into the Christmas tree, in part because Christmas trees were typically not salvaged. Alternatively, some prior art methods have to mobilize coil tubing to protect the tree, which typically increases overall costs.
U.S. Pat. No. 4,241,786 issued to Bullen for xe2x80x9cWELL TREE SAVERxe2x80x9d is illustrative and teaches a bypass attachment to prevent damage to the valves of a Christmas tree when fluid at high pressure is passed into a well, such as during a fracturing process. The bypass attachment is formed of a piston rod removably mounted to the well tree and offset from it, a piston mounted on the piston rod, a cylinder movable on the piston, the cylinder bearing a piece of high-pressure tubing aligned with the passage through the well-head tree, a high-pressure valve to close off the high-pressure tubing and sealing means to seal the space between the exterior of the high-pressure tubing and the interior of the vertical passage through the well-head tree. There is no suggestion, motivation, or teaching to use pressure to lower a tree saver into place or to position the tree saver into a predetermined position extending into a tubing hanger associated with the tree.
The prior art does not teach use of pressure to lower a tree saver into place or to position the tree saver into a predetermined position extending into a tubing hanger associated with the tree. Further, the prior art does not teach a tree saver that is wireline set and retrieved or pressure set and retrieved.